2004

Use Coordinates and Coordinate Systems | 227
In practice, most coordinates are entered relative to the UCS rather than the
WCS.
Control the User Coordinate System in 3D
You define a user coordinate system (UCS) to change the location of the 0,0,0
origin point and the orientation of the XY plane and Z axis. You can locate
and orient a UCS anywhere in 3D space, and you can define, save, and recall
as many UCSs as you require. Coordinate input and display are relative to the
current UCS.
UCSs are especially useful in 3D. You may find it easier to align the
coordinate system with existing geometry than to figure out the exact
placement of a 3D point.
If multiple viewports are active, you can assign a different UCS to each view-
port. With the
UCSVP system variable turned on, you can lock a UCS to a
viewport, automatically restoring the UCS each time that viewport is made
current. With
UCSVP turned on, each UCS can have a different origin and
orientation for various construction requirements.
Define the UCS Location
You can define a UCS in several ways:
■ Specify a new origin, new XY plane, or new Z axis.
■ Align the new UCS with an existing object.
■ Align the new UCS with the current viewing direction.
■ Rotate the current UCS around any of its axes.
■ Apply a new Z-depth to an existing UCS.
■ Apply a UCS by selecting a face.
Use UCS Presets
If you do not want to define your own UCS, you can choose from several
preset coordinate systems. The images on the Orthographic UCSs tab of the
first UCS second UCS
model with both UCSs